a) Field of the Invention
The invention relates to a method for measuring electrical variables (e.g. DC or AC voltages or currents, powers or resistances), in a conductor, without contacting the conductor.
b) Description of Related Art
Conventionally, determination of current in electrical conductors is accomplished in a non-touching manner with an adapter intended to surround the conductor as completely as possible. If a coil system is associated with a magnetically permeable material which substantially surrounds the conductor through which current flows, a variable which is proportional to the current in the electrical conductor is induced in such a coil system and, as a result of the known proportionality of the induction current to the measurement variable, determination of current strengths without physical contact is possible. To determine direct currents with the aid of such adapters, the current measurement is based on a magnetic field measurement using Hall probes or magnetization characteristic probes. However, these probes have disadvantages with respect to offset, noise and temperature errors. Another disadvantage of this method is that it can be carried out only when the conductor in which the current to be determined is substantially surrounded.
It is known that electromagnetic alternating fields in coils induce signals which can be used to produce different indications. A quantitative determination of the measurement variable itself is generally not directly possible owing to the lack of suitable reference fields.
IBM Technical Disclosure Bulletin, Vol. 10, No. 7, December 1967, page 876 discloses a coil system to be set into mechanical oscillation in order to amplify very small direct currents and DC voltages. Australian publication AV-B-471 986 discloses a magnetometer in which a conductor is set into oscillation and the signal induced by a magnetic field is measured.